1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device by using a doping technique.
2. Description of the Related Art
As one step for manufacturing a semiconductor device, there is an ion injection step. The ion injection step is performed when forming source and drain regions in a semiconductor film, when forming a low-concentration impurity region containing an impurity at low concentration, or the like. For manufacturing one semiconductor device, ion injection steps in various conditions are required. For example, various kinds of ion injection steps are performed for manufacturing a semiconductor device in Patent Document 1.
In a present manufacturing process of a semiconductor device, a doping apparatus in which plasma is generated by arc discharge using a filament has been frequently used. This doping apparatus has been widely used because of the high-current density and easy application for a large-size substrate as compared with a conventional RF-discharge type doping apparatus. A filament is an electron generating means, and plasma is generated by applying voltage between an anode and the filament which is a cathode.    [Patent Document 1] Japanese Patent Laid-Open No. 2000-349298
In general, when ion injection is performed in various conditions in a manufacturing process of a semiconductor device, a plurality of doping apparatuses is used. For example, ion injection is performed at low concentration with a first doping apparatus, and then a substrate is moved into a second doping apparatus so that ion injection is performed at high concentration. However, the doping apparatus is required to be provided in number corresponding to the number of ion injection steps, thus, a plurality of doping apparatuses is required to be provided. In addition, substrate size has been increased in recent years and correspondingly, a doping apparatus has also been increased in size.
In such a situation, floor space of a factory is occupied by the ion doping apparatus, and there has been a problem that a manufacturing line cannot be constructed well. In addition, the number of apparatuses to be provided cost much.
On the other hand, when ion injection in various conditions is performed with the same doping apparatus in order to suppress the number of apparatuses, there has been another problem that a filament (also called an electron generating means) deteriorates in an arc discharge doping apparatus. In particular, the filament has deteriorated significantly in setting up for the next doping step performed with a lower filament current.
This is because the filament temperature also decreases along with the decrease of the filament current, and when the filament temperature becomes lower than the boiling point of an element contained in a material gas, the element becomes liquid near the filament so that it penetrates and deteriorates the filament. Therefore, in the case where ion injection is performed in various conditions with the same doping apparatus where filament deterioration occurs, it is necessary to replace the filament regularly, therefore, there has been a big problem of reduction of such down time.
Further, a material gas with high concentration has been used recently in many cases, which has escalated the problem of filament deterioration.